Search and rescue teams could continue looking for survivors for a second night following yesterday's Christchurch earthquake, Civil Defence national controller David Coetzee says.

The death toll sits at 75, and hundreds more are reported missing.

Mr Coetzee said the search for survivors was not expected to be completed tonight. "It will be completed as these teams work through it. They will not stop until they go through it," he said.

The search and rescue teams are focusing on 10 buildings considered critical where people could be trapped inside.

The search may be painfully slow, he said, but "they have to find the people, locate them and then work out what is the best way to reach them".

The Government declared a national state of emergency this afternoon, and Civil Defence director John Hamilton was heading down to Christchurch to work with the local Civil Defence team.

Civil Defence Minister John Carter said the earthquake was huge task for the local authority, and would need the support of Civil Defence headquarters.

"We will be bringing in people from around the country who have Civil Defence expertise to work in there and work alongside the people of Canterbury, just to make sure that everything is giving them the help they need."

He could not say how long the state of emergency would last.

"It's really hard to know yet. We haven't got sufficient information to actually know yet what's happened exactly. It's too early."

Mr Coetzee said a national action plan would be developed, which was expected to be ready tomorrow.

"It will set the strategic direction. It will set the priorities for a specific operational period. Under that the council will develop their own plans.

"It just ensures that everything is sync and everybody responds from the same page."

He said hundreds were being deployed to help, including seven local response teams from across New Zealand.

Building inspectors, engineers, sewage crews and staff to assist with operations are also making their way to Christchurch.

Defence Minister Wayne Mapp said there were about 1000 defence personnel deployed, including the people from navy vessel HMNZS Canterbury.

"In fact the Canterbury is going to be providing 1000 hot meals tonight for the people of Lyttelton," he said.

There was also a disaster assistance and relief team of 55 people from Singapore arriving tonight, and 198 people from the United States, Japan, and the United Kingdom arriving tomorrow.

Mr Coetzee said water containers and trucks were being sent to people in need.

"We are assessing the need. We have international offers that we have to work through the councils."

He said there was a defence 757 plane flying between Christchurch and Wellington with the purpose of getting people out.

The planes take up to 100 people per flight, and a centre has been set up at Wellington Airport today where people are being received.

"The intent of that is to free up accommodation space in Christchurch which is one of our challenges."

He said he was finding accommodation for the people who are being deployed to help.

National state of emergency

Prime Minister John Key said the quake had brought "death and destruction on a dreadful scale".

He said there was no question the earthquake would have a significant economic impact on Christchurch and New Zealand, given the damage to the city's CBD.

The central city was likely to be out of action for some time.

"We're going to have to go back and reassess every building."

Mr Key said the first earthquake was estimated to have cost between $6bn and $8bn. Initial advice suggested the bill for yesterday's quake would be far more costly.

"We can afford that," said Mr Key but he said it would put a dent in the EQC's and the Government's resources.

Following this morning's media briefing, Mr Key planned to immediately head back to Christchurch.

Declaring a national state of emergency is an option when a disaster or other event is or is likely to be of such severity that it is beyond the resources of the local Civil Defence groups.

It provides for a national resources to be marshalled to perform emergency functions and tasks such as:

* rescues
* evacuations from dangerous areas and the closing off of buildings, homes and other premises, public places and roads.
*setting up first aid posts
*providing relief such as emergency food, clothing and shelter
*regulating road, air and sea traffic
*undertaking the emergency disposal of bodies

It also allows authorities to requisition any land, building, vehicle, animal, boat, equipment, construction materials, bedding, food and medical supplies considered necessary for the preservation of human life.

New Zealand flags are flying at half mast on all Government buildings today to honour the victims of yesterday's devastating quake in Christchurch.

Mr Key requested the flags on all public buildings be half-masted indefinitely.

The gesture is intended as a mark of respect for those who have been killed, injured or left with damaged homes.